Kilgallon is expected to be sidelined for the remainder of the season after surgery on a damaged pectoral muscle last weekend.
Nathaniel Knight-Percival (ankle) and Alex Jones (hip) will both need to be assessed ahead of the Gillingham game to see if they have a chance of featuring.
All four of City's deadline day signings - Charlie Wyke, Kevin Toner, Jacob Hanson and Matthew Penney - are in contention for places in McCall's match-day squad after joining in with training this Thursday.
McCall says Rory McArdle will also be up for selection despite requiring stitches in a head wound during Tuesday's Checkatrade Trophy tie at Oxford United.
The City chief said: "Nat (Knight-Percival) and (Alex) Jonesy have done some work with the physio.
"As long as they don't have any adverse reaction to any of that, the hope is to have them available and raring to go for Saturday.
"Rory (McArdle) had five stitches right on his eyebrow but he'll be fine for Saturday.
"He is a warrior - he'll be 100% fit and raring to go for Saturday if selected.
"Matthew's surgery last weekend was a success but he will need to have his arm in a sling for the next few weeks.
"He has been back in the training ground today (Thursday). It was great to see his face around the place again because he is a popular lad.
"It was obviously a big blow to lose him to injury but unfortunately that sometimes happens in football.
"It was good to see Jacob Hanson and Matthew Penney get a game under their belts in the reserves on Wednesday. They both put in really strong performances.
"Charlie (Wyke) and Kevin Toner had their first training session with the club this morning.
"We have a good dressing room at the club - a great bunch of people - so it has been nice to get the new lads integrated quickly."